public class MyLinkedList {
    // 2、无头双向链表实现
    static class ListNode{
        int val;
        ListNode prev;
        ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    }
    ListNode head;
    ListNode last;
        //头插法
        public void addFirst(int data){
            ListNode node = new ListNode(data);
            if(head == null){
                head =last = node;
            }else {
                node.next = head;
                head.prev = node;
                head = node;
            }
        }
        //尾插法
        public void addLast(int data){
            ListNode node = new ListNode(data);
            if(head == null){
                head =last = node;
            }else {
                node.prev = last;
                last.next = node;
                last = last.next;
            }
        }
        //任意位置插入,第一个数据节点为0号下标
        public void addIndex(int index,int data){
            int len = size();
            try{
                checkIndex(index);
                if(index == 0){
                    addFirst(data);
                    return;
                }
                if(index == len){
                    addLast(data);
                    return;
                }
                ListNode cur = head;
                ListNode node = new ListNode(data);
                for (int i = 0; i < index; i++) {
                    cur = cur.next;
                }
                node.next = cur;
                node.prev = cur.prev;
                cur.prev.next = node;
                cur.prev = node;
            } catch (PosIllegal e){
                e.printStackTrace();
            }


        }

        private void checkIndex(int index){
            int len = size();
            if(index < 0 || index > size()){
                throw new RuntimeException("index位置不合法");
            }
        }
        //查找是否包含关键字key是否在单链表当中
        public boolean contains(int key){
            ListNode cur = head;
            while(cur != null){
                if(cur.val == key){
                    return true;
                }
                cur = cur.next;
            }
            return false;
        }
        //删除第一次出现关键字为key的节点
        public void remove(int key){
            ListNode cur = head;
            while(cur != null){
                if(cur.val == key){
                    if(cur == head) {
                        head = head.next;
                        if (head != null) {
                            head.prev = null;
                        }
                    }
                    else {
                        cur.prev.next = cur.next;
                        if(cur == last){
                            last = last.prev;
                        } else {
                            cur.next.prev = cur.prev;
                        }
                    }
                    return;
                }
                cur = cur.next;
            }
        }
        //删除所有值为key的节点
        public void removeAllKey(int key){
            ListNode cur = head;
            while(cur != null){
                if(cur.val == key){
                    if(cur == head) {
                        head = head.next;
                        if (head != null) {
                            head.prev = null;
                        }
                    }
                    else {
                        cur.prev.next = cur.next;
                        if(cur == last){
                            last = last.prev;
                        } else {
                            cur.next.prev = cur.prev;
                        }
                    }
                }
                cur = cur.next;
            }
        }
        //得到单链表的长度
        public int size(){
            ListNode cur = head;
            int len = 0;
            while(cur != null){
                len++;
                cur = cur.next;
            }
            return len;
        }
        public void display(){
            ListNode cur = head;
            while(cur != null){
                System.out.print(cur.val + " ");
                cur = cur.next;
            }
            System.out.println();
        }
        public void clear(){
            ListNode cur = head;
            while (cur != null){
                ListNode curNext = cur.next;
                cur.prev = null;
                cur.next = null;
                cur = curNext;
            }
            head = last = null;
        }

}
